What is a DBMS? Types of Databases

Plain text file vs relational database

In short: what’s the difference

A plain text file stores data as a set of lines with no built-in rules: who changes a row and when is up to the application. A relational database stores data in tables with a schema, keys, and integrity constraints. So a text file fits simple local tasks, while a relational DB fits multi-user systems where correctness, relationships, and predictable queries matter.

Plain text file: no schema or built-in integrity control

Relational DB: tables, types, PK/FK, and constraints

Files — for simple scenarios; DB — for business-critical data

SQL gives structured queries and reliable links between entities

Switch the mode (Plain Files / Relational DB buttons) and click a row

users

id	name
1	Mike
2	Anna

courses

id	title	price_rub
101	SQL Basics	600
102	Java Core	800
103	PostgreSQL Pro	900
104	Spring Boot: API	1100
105	Docker for Backend	700

enrollments

id	status	user_id	course_id
9001	paid	1	101
9002	paid	2	102
9003	paid	2	104

In “File” mode, data looks like separate fragments with no single set of rules: relationships between the “users”, “courses”, and “enrollments” tables are not checked automatically — duplicates and inconsistent rows are easy to get.

The DBMS as guarantor of correctness

A DBMS (database management system) introduces transactions: a set of operations is either fully committed or rolled back. At the same time, row locks and data versions work in parallel: while one session changes a balance, another waits or reads a consistent state — not an “old copy from a file.” Picture the DBMS as a bouncer at the data door: without a queue, rule checks, and a log, no one blindly rewrites critical amounts.

Glossary: database, DBMS, transaction, concurrent access

These four definitions are foundational. Learn them together: data lives in the DB, the DBMS guards it, a transaction defines an all-or-nothing boundary, and concurrent access is about many clients at once without corrupting integrity.

Database — an integrated collection of structured data stored together with minimal redundancy.

DBMS — software for creating, maintaining, and shared use of a database by many users.

Transaction — the smallest logical unit of work that runs entirely or not at all.

Concurrent access — the DBMS’s ability to serve many users at once without breaking integrity.

Takeaway: a DBMS is a reliability mechanism for data. It defines the schema, validates relationships, manages concurrent access, and protects integrity on changes. A text file stores characters; a DBMS manages the data lifecycle.